lindex.n

tcl是工具命令语言

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'\" Copyright (c) 1993 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
'\" Copyright (c) 2001 by Kevin B. Kenny.  All rights reserved.
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'\" RCS: @(#) $Id: lindex.n,v 1.7 2001/11/14 23:15:33 hobbs Exp $
'\" 
.so man.macros
.TH lindex n 8.4 Tcl "Tcl Built-In Commands"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
lindex \- Retrieve an element from a list
.SH SYNOPSIS
\fBlindex \fIlist ?index...?\fR
.BE
.SH DESCRIPTION
.PP
.VS 8.4
The \fBlindex\fP command accepts a parameter, \fIlist\fP, which
it treats as a Tcl list. It also accepts zero or more \fIindices\fP into
the list.  The indices may be presented either consecutively on the
command line, or grouped in a
Tcl list and presented as a single argument.
.PP
If no indices are presented, the command takes the form:
.CS
lindex list
.CE
or
.CS
lindex list {}
.CE
In this case, the return value of \fBlindex\fR is simply the value of the
\fIlist\fR parameter.
.PP
When presented with a single index, the \fBlindex\fR command
treats \fIlist\fR as a Tcl list and returns the
.VE
\fIindex\fR'th element from it (0 refers to the first element of the list).
In extracting the element, \fBlindex\fR observes the same rules
concerning braces and quotes and backslashes as the Tcl command
interpreter; however, variable
substitution and command substitution do not occur.
If \fIindex\fR is negative or greater than or equal to the number
of elements in \fIvalue\fR, then an empty
string is returned.
If \fIindex\fR has the value \fBend\fR, it refers to the last element
in the list, and \fBend\-\fIinteger\fR refers to the last element in
the list minus the specified integer offset.
.PP
.VS 8.4
If additional \fIindex\fR arguments are supplied, then each argument is
used in turn to select an element from the previous indexing operation,
allowing the script to select elements from sublists.  The command,
.CS
lindex $a 1 2 3
.CE
or
.CS
lindex $a {1 2 3}
.CE
is synonymous with
.CS
lindex [lindex [lindex $a 1] 2] 3
.CE
.SH EXAMPLES
.CS
lindex {a b c}  => a b c
lindex {a b c} {} => a b c
lindex {a b c} 0 => a
lindex {a b c} 2 => c
lindex {a b c} end => c
lindex {a b c} end-1 => b
lindex {{a b c} {d e f} {g h i}} 2 1 => h
lindex {{a b c} {d e f} {g h i}} {2 1} => h
lindex {{{a b} {c d}} {{e f} {g h}}} 1 1 0 => g
lindex {{{a b} {c d}} {{e f} {g h}}} {1 1 0} => g
.CE
.VE
.SH "SEE ALSO"
list(n), lappend(n), linsert(n), llength(n), lsearch(n), 
.VS 8.4
lset(n),
.VE
lsort(n),
lrange(n), lreplace(n)

.SH KEYWORDS
element, index, list